Brick and tile products make up a significant segment of the basic structural components utilized by the construction industry. Brick is well established as a long lasting, weather resistant and structurally sound component for both residential and commercial buildings and has changed relatively little in structural properties over the many years it has been in use.
Bricks are used for buildings, pavings, and for decorative surfaces. Other tile products which are commonly used in the building trades, and which are formed of clay as a basic component, include clay pipes, clay tiles, roof tiles, ceramic tile and the like. While the types of clay used for the various bricks and tile differ somewhat, the principal component is clay, which has been appropriately beneficial and mixed with other additives conducive to proper binding, color, texture and the like.
Common brick measures approximately 2".times.4".times.8", and it and other tile products have a typical density of about 120-130 pounds per cubic foot. Brick is not regarded as an effective insulator with its R value of approximately 0.70 for the standard thickness of a dry brick. This insulative factor drops even more when the brick has absorbed significant water as is common due to the high permeability of most unglazed brick.
Brick is manufactured from clay or shale which is subsequently refined and fired in a kiln to produce a hard, polycrystalline building product. While refined clay is the principal solid material for brick manufacture, it is supplemented by grog, minerals, binders and other inorganic oxides, to which water is added. Individual bricks are made by either a soft mud method by which the brick is molded to shape by hand or machine, or by the stiff mud process in which the brick is extruded through a die under high pressure and wire cut to the proper size. After forming, the bricks are dried under controlled conditions in order to keep the brick from breaking during removal of the water. Firing of the bricks is then accomplished by placing the product in a kiln and subjecting it to a thermal process whereby solid state sintering occurs in the 1100 to 1200 degree centigrade range. Clay tiles, pipes and other clay products also undergo similar firing in kilns to achieve the desired polycrystalline composition which produces the desired physical properties of the products.
A major shortcoming of all the described brick and tile products is their substantial weight and the resulting high cost of shipping the product. While the manufacturing cost of brick is relatively low, a point is reached where the cost of shipping adds so much to final delivered cost as to limit the effective marketing area of a manufacturing facility. Some efforts have been made to reduce the weight or density of brick, but the resulting product has had sufficient deficiencies as to greatly restrict its uses and has not been well received commercially. For example, volatile or burnable substances, such as sawdust, have been added to clay mixes so that during thermal processing the sawdust or other substance volatilizes and is driven off as a gas. U.S. Pat. No. 4,123,284 to Konrad C. Rieger summarizes the various efforts to make ceramic bodies lighter and suggests a mechanical agitation method utilizing clay and pyrophyllite as a way to achieve more uniform porosity. The result is an exceptionally porous brick which is lighter, but which is filled with cavities or voids from which the sawdust has been burned away. Such brick is generally softer and less weather resistant than ordinary brick. It is much more vulnerable to water absorption, and if exposed to inclement weather, the voids can fill with water and significantly increase the weight of the brick. In colder climates, such water can freeze and significantly speed up the breaking and degeneration of the brick. With these shortcomings, such brick is not well suited for outdoor use.
The use of lightweight, high quality brick, were it available, could also achieve significant cost reductions and time savings in building construction. For example, an oversized and heavier brick measuring 4".times.4".times.12" and known as "economo" brick is used extensively in commercial construction. Because of its weight, little more than a four foot high section of such economo brick can be constructed without waiting for the mortar to harden, or the brick's great weight produces unwanted settling and sag of the courses. When the four foot height has been reached, workmen must move to a new work site, move scaffolding, brick supplies and mortar to the new site and begin a new section of wall. After the first section has set or hardened, the movement must be reversed and work resumed on the first section. Typically, economo brick is erected in nine foot high sections, with each section being supported on a steel lintel carried by the steel building frame. Accordingly, it would be desirable to have a economo brick which is light enough to be erected in nine foot sections without allowing hardening time for mortar joints. Availability of such a lightweight economo brick would speed up construction and reduce wasted labor costs.
Most modern buildings have rigid, heavy steel framework sized to support the estimated weight of the building and all building components and contents thereof. Were it possible to significantly decrease the weight of the brick and clay tile products, steel framework could be commensurately lighter and less expensive in accord with the reduction in brick weight. For example, were it possible to introduce an acceptable lightweight brick or tile product to replace those now surrounding the elevator shafts of large office buildings, the costs of steel and footings required for the shafts could be reduced by one to two million dollars per building. Further reduction in construction costs would be possible due to lower shipping charges associated with transportation of brick and other fired products.
Another shortcoming of commercially available, unglazed brick is its high porosity and permeability to water. High porosity is undesirable because it permits the brick to absorb water under heavy rainfall or high humidity conditions, and the presence of such water in the brick further increases the significant weight of the brick and further diminishes the marginally adequate insulative properties of the brick. Dry brick is far less heat conductive than wet brick. Face brick having a side to side width of approximately four inches has an R value of approximately 0.4 when dry. The R value may drop still further when the brick has absorbed significant quantities of water. In colder winter climates where R values are important, such high water content also expose the brick to more rapid deterioration from internal ice damage produced by frequently recurring melting and freezing cycles. Accordingly, it is highly desirable that brick be made less permeable.
The present invention provides a sintered polycrystalline building product including brick and other fired products which are dramatically lighter in weight, while having significantly improved thermal and acoustical insulation characteristics and greatly reduced permeability. These goals are accomplished by changing the composition of the fired products by replacing substantial portions of the now used clay with inexpensive, ceramic microspheres having random diameters typically under 200 microns in diameter.
It is known to manufacture hollow glass microspheres, and such spheres have been used in some non brick and non fired products. For example, glass microspheres have been used as a component in auto body filler compounds of the type used in repairing dents and abrasions and as a filler in plastics and joint compound of the type used for dry wall work. Glass microspheres have been added to a cementitious foundational wallboard of the type used as an underlayment for tile. As illustrated in U.S. Pat. No. 4,380,569, glass microspheres have been used in cushions and floor mats. U.S. Pat. Nos. 4,079,162 and 3,045,709 show use of glass microspheres in resins for sound attenuation and thermal insulation, respectively. In U.S. Pat. No. 4,492,732, glass microspheres have been used in curable thermo resins as a lightweight material to fill cavities in boats and aircraft. Such microspheres have been added to powders during flame spraying to create a thermal barrier as described in U.S. Pat. No. 4,303,737. Such glass microspheres have also found utilization as a component in types of particle board for improving thermal and acoustical insulation properties. The glass microspheres would not be usable in sintered products, however, since such glass spheres have softening and melting points well below the temperatures at which brick and tile are fired. Any attempt to use them would produce a poor and unusable brick due to the melting of the microspheres and resulting in the weakening of the brick as the spaces occupied by such spheres collapse or fracture due to excessive pressure buildup within the spheres caused by the heating. Such bricks would be more prone to fracturing and have extensive and sometimes unpredictable shrinkage.
Several companies manufacture high quality ceramic microspheres having melting points above the temperatures required for firing of brick and tile, but the cost of such quality microspheres has been far beyond the range tat would ever permit their use in brick. For example, such ceramic microspheres have been priced at about 83 cents or more per pound in quantities of twenty or more tons and, if used as a major ingredient of common brick, could raise the price of ingredients for each brick by approximately $1.20. There would be little commercial interest in brick were the price of each brick to increase from current levels of thirty to forty cents per brick to $1.50. These commercially available, high quality ceramic microspheres, in tests by this inventor, have also had mixing problems in combining clay with the microspheres and resulted in poor quality brick which cracked badly.
Another source of microspheres has been recognized in recent years with such spheres being discovered in the fly ash residue of many coal burning electric power plants. The microspheres produced at such power plants have been generally regarded as low grade and as a troublesome residue which has often been unused or used for landfill. Such fly ash microspheres are generally regarded as low grade product because they have random characteristics in diameter, wall thickness and other properties. Some of these microspheres are quite heavy for their size and others are hollow and light enough to float on the surface of settling ponds. The residue has been used at times as an extender in epoxy paints and some adhesives. Cement plants which burn coal and thus produce fly ash as a residue have used the residue and the microspheres therein as a filler or additive for cement, but no use has been made of such fly ash and residue that requires the application of high heat, and few commercial applications have been found for them. Such microspheres have not been used for production of brick or other fired building products. The perceived properties of these power plant microspheres have been described in U.S. Pat. No. 4,115,256 and in an article by H. Jan de Zeeuw and Roland V. Abresh entitled, "Cenosoheres From Dry Fly Ash", and presented at the Third International Ash Utilization Symposium in 1973. The present invention utilizes these random characteristic power plant microspheres which the inventor has found to possess average melting points above the temperatures required for firing of brick and tile products. The low grade and random properties of these microspheres make them available at prices well below that of even traditional clays used in brick manufacture, making it feasible to manufacture improved, superior brick and other fired crystalline products at costs comparable to and sometimes lower than traditional fired products formed of clay.